Apparatus for the electrolytic polishing of limited surface portions of a metallic workpiece



Aug. 19, 1958 2,848,410

. E. C. F. KNUTH-WINTERFELDT ETAL APPARATUSES FOR THE ELECTROLYTICPOLISHING 0F LIMITED SURFACE PORTIONS OF A METALLIC WORKPIECE FiledApril 30, 1956 2 Sheets-Sheet l INVENTORJ Eeczwr C. F. Kmma -Wnmzm=sunLnumrz G, Dame R1? MM M rm ATTORNEYS Aug. 19, 1958 2,848,410

E. C. F. KNUTH-WINTERFELDT ETAL APPARATUSES FOR THE ELECTROLYTICPOLISHING OF LIMITED SURFACE PORTIONS-OF A METALLIC WORKPIECE FiledApril 30, 1956 2 Sheets-Sheet 2 Fig.

INVENTORS EGGERT CHI-T KNUI'H VmTERFeLm LAURITZ C DANG/MRI) BY m, M, M 9#2123,

ATTORNEYS United States Patent Ofiice 2,848,410 Patented Aug. 19, 1958APPARATUSES FOR THE ELECTROLYTIC POLISH- ING OF LIMITED SURFACE PORTIONSOF A METALLIC WORKPIECE Eggert Christian Flemming Knuth-Winterfeldt,Gentofte, and Lauritz Gndmund Damgaard, Virum, Denmark, assignors to H.Struers Chemiske Laboratorium, Copenhagen, Denmark This inventionrelates to an apparatus for the electrolytic polishing of limitedsurface portions of a metallic workpiece for the purpose of subjectingthe polished area to a structure test. This method is used to anincreasing extent for the testing of materials and construction parts.

The principle of electrolytic polishing is that the surface area to bepolished is brought into contact with an electrolyte, whereafter apotential difference is created between the workpiece and an electrodein the electrolyte. Moreover, to obtain a uniform polishing it isimportant that during the electrolytic process there should be a certainflow motion of the electrolyte relative to the surface area to bepolished.

To fulfill these conditions, apparatuses have been used for electrolyticpolishing, having a mouthpiece to be applied in contact with theworkpiece, and means for conducting an electrolyte to and from themouthpiece as well as means for creating a potential difference betweenthe electrolyte and the workpiece.

In some known apparatuses of this type, the mouthpiece is mounted on astationary equipment comprising a tank and circulation pump for theelectrolyte as well as electrical equipment for creating the potentialdifference. In apparatuses of this type, it is possible to construct themouthpiece and the circulation path of the electrolyte in such a mannerthat a relatively great area can be swept in a satisfactory manner witha flowing electrolyte, so that a uniformly polished spot of -relativelygreat size can be obtained. However, these apparatuses have the drawbackthat only relatively small workpieces can be polished, because thesemust be clamped to the mouthpiece. This again means that the apparatusesinquestion are only suitable for the testing of samples of material, e.g. cut out of construction parts in a running production, but ordinarilynot for the so called intact testing of the workpieces themselves.

On the other hand, it has been proposed for intact testing purposes touse a mouthpiece in the form of a pipette, which is applied to the workpiece at the spot where the latter is to be polished, and to which anelectrolyte is supplied through a flexible tube and is thereafterpermitted to flow ofi freely from the point of contact between theworkpiece and the pipette, the mouth of which may be speciallyconstructed for the purpose of obtaining auniform and controlled flowoff. With this apparatus, a great flexibility of application and fullpossibility of intact testing are obtained, but on the other hand, it isonly possible to produce a very small polished spot, which is far toolimited for certain examinations.

The present invention relates to an apparatus of the same type as abovedescribed, and it is the object ofthe invention to construct anapparatus of this type in such a manner as to obtain the sameflexibility of application and the same possibility of intact testing aswith the apparatuses last described, while still extending the polishing to an area of the same order of size as with the apparatuses firstdescribed.

To achieve this, according to the invention, the mouthpiece is mountedon a handle, which is connected with a source of electrolyte throughflexible liquid conduits and is provided with an operating member forcutting off the supply and discharge of electrolyte to and from themouthpiece.

With an apparatus of this construction, the workpiece must not beclamped to the mouthpiece, but the latter will simply be pressed againstthe workpiece by means of the handle on which it is mounted. It istherefore possible to polish an existing workpiece at any place thereofwithout damaging the workpiece, i. e. there is full possibility ofintact testing. On the other hand, there exists a two-way circulationpath for the electrolyte so that it becomes possible to cause the latterto sweep a relatively great area uniformly within the circumference ofthe mouth piece, whereby it again becomes possible to produce aconsiderably greater polished area than with the pipette apparatuses.The correspondingly greater quantity of the electrolytic liquid thatmust be caused to flow in the mouth piece is returned through a returnconduit and thus does not have to drip off from the operating position.Consequently, the waste of electrolyte and the drainage of the latter tothe surroundings of the testing spot, which is characteristic of thepipette apparatuses, and which would be of great disadvantage inapparatuses for the polishing of greater areas with use of correspondingquantities of electrolyte, are avoided. It is also important that anoperating member for cutting off the supply and discharge of electrolyteto and from the mouthpiece is provided on the handle itself, because itbecomes thereby possible to start the circulation of the electrolyteonly in the moment the mouthpiece has been correctly applied to theworkpiece, even if in this moment the handle should be relatively remotefrom the other equipment employed.

According to the invention, the mouthpiece may advantageously be mountedon the handle by means of an articulated joint, whereby the mouthpiecewill be capable more easily of applying itself sealingly to theworkpiece than if it were rigidly connected with the latter. Accordingto one method of constructing the said articulated joint, the mouthpieceis mounted on a pin which is rotatably mounted in the handle forrotation about an inclined axis intersecting the axis of the mouthpiecein a point in the vicinity of the face of the mouthpiece to be appliedto the workpiece. This construction provides a simple means of obtaininga secure and stable engagement of the mouthpiece with the surface of theworkpiece.

To obtain the cutting ofi of supply and discharge of electrolyte to andfrom the mouthpiece, the flexible liquid conduits may be in the form offlexible tubes extending from'the mouthpiece through the handle, asqueezing member operated by the said operating member being provided inthe handle and serving to squeeze the flexible tubes.

With particular advantage, the squeezing means may be'arranged toperform, in the operation of squeezing the flexible tubes, a sweepingmovement longitudinally of the latter in a direction away from themouthpiece. By this means the tendency to dripping from the mouthpieceafter the circulation of electrolyte therethrough has been stopped isminimized.

In order that the squeezing member should subject the flexible tubes toas little wear as possible while squeezing and sweeping along thelatter, the squeezing member may preferably be in the form of a roll,which is mounted at the end of a lever mounted in the handle and formingthe operating member.

For the purpose of facilitating the operation, the said lever may 'bebiased by means of a spring tending to turn the lever in a directiontoward "the squeezing position, the said spring being arranged in such amanner that the moment arm on which it acts becomes shorter when thelever is turned away from the squeezing position. The advantage of thisis that in the resting position, in which the lever is to be kept whilethe electrolytic polishing is being performed, it will only be subjectedto a relatively small biasing torque so that it'requires little force tohold the lever in this position, while on'the other hand in the positionwhere the lever is to squeeze the flexible tubes it is subjected to astrong biasing'torque so as to etfect a powerful squeezing'under theinfluence of the spring.

The manner in which the liquid is caused to flow in the mouthpiece isvery important in order to obtain the best results. It has been 'foundthat the principles of flow which have previously been used inapparatuses with a stationary mouthpiece are not directly suitablefor'adoption in the apparatus here concerned. It has been found that anadvantageous type of flow giving a uniform polishing can be obtained ifthe mouthpiece is constructed with two 'co-axial passages opening at asmall'distance behind the face of the mouthpiece to be applied to theworkpiece, the outer meat which passages is connected with the supply,while the inner passage is connected to the discharge for theelectrolytic liquid. The inwardly directed flow of the electrolyteobtained in this manner has been found to be far superior to theoutwardly directed flow which is frequently used in apparatuses withstationary mouthpiece and also in'the above mentioned apparatuses withpipette. To obtain the best possible results it has been foundadvantageous to provide guiding means imparting a circular movement tothe incoming electrolytic liquid at the opening ofthe outer one of theco-axial passages.

To enable the mouthpiece to fit as closely as possible to the surface ofthe work piece, it is proposed according to the invention to constructthe mouthpiece in such a manner that the wall of the part of 'themouthpiece extending beyond the mouths of the co-axial passagesconsn'tutes an elastic sleeve.

Preferably, the arrangement should be such that the electric circuit canonly be completed when the mouthpiece has been applied to the workpieceand the flow of electrolyte has been started. To obtain this, accordingto the invention, the operating member on the handle may be adapted,towards the end of its movement for setting free the flow of electrolyteto and from the-mouthpiece, to close a contact in the electriccircuit'for estab-' lishing the required potential difference betweenthe electrolyte and the workpiece.

As mentioned, the flexible conduits from the handle should be connectedto a source of electrolyte during the use of the apparatus from whichsource a circulation of electrolyte through the flexible conduits andthe mouthpiece should be caused.

In many cases, the laboratory or workshop using the apparatus accordingto the invention will already have available an apparatus of the abovedescribed type with a stationary mouthpiece, and in that case the handlewith the mouthpiece and the flexible conduits may be used as anattachment to the existing apparatus, the flexible conduits beingconnected to the electrolyte circuit of the existing apparatus insuitable manner. The latter also supplies the necessary potentials tothe work piece and to an electrode provided in the handle. However, asfar as the electrolyte circuit is concerned, it is frequentlyadvantageous to be independent of other apparatuses for producing thecirculation of electrolyte, among other things in order to obtain agreater flexibility of use and independence of the pressure levelywhichan existing apparatus is capable of supplying. The invention thereforealso relates to simple means for creating a flow of electrolyte throughthe flexible conduits and'the :mouthpiece. According to this aspect ofthe invention, the flexibleconduits from the handle are'connectedindividually to two tanks which are mounted in a case in such a mannerthat in one position of the latter there is created a difference oflevel between the tanks, causing electrolyte to flow from one tankthrough the mouthpiece to the other tank, while in another position ofthe case an opposite difference of level between the tanks is createdcausing a return flow of electrolyte from the second to the first tankthrough a direct conduit connection between the two tanks provided forthis purpose.

By making oneself independent of other apparatuses for causing thecirculation of electrolyte, it becomes also possible to operate at apressure below that of the atmosphere in the mouthpiece so that theelectrolyte is not inclined to drain off if the handle happens to belifted from the workpiece during the process. For this purpose,according to one embodiment of the invention, the flexible conduits fromthe handle are individually connected to two tanks, one of which issealingly closed and provided with a rubber ball or the like means forsubjecting the tank .to a slight pressure or vacuum, while the othertank is in open communication with the atmosphere, a conduit connectionbeing provided between the two tanks and comprising a valve, which onlypermits a flow of liquid in the direction from the closed towards theopen tank.

The invention will now be described in further detail with reference tothe accompanying drawing, in which:

Fig. l diagrammatically shows a longitudinal section through one form ofa handle with mouthpiece and combined liquid flow interrupter andelectrical switch forming part of an apparatus according to theinvention,

Fig. 2 on a larger scale a longitudinal section through the mouthpiece,

Fig. 3 the mouthpiece of Fig. 2, as viewed from the bot tom,

Fig. 4 a developed section along the line lV-IV of Fig. 2,

Fig.5 diagrammatically one form of a case with tanks for causing theflow of electrolyte, as viewed in its operating position,

Fig. 6 the same as viewed in its position of transportation, and

Fig. 7 another form of an equipment for causing the flow of electrolyte.

In the drawing, 1 is a handle, which at its front end is constructedwith an inclined bore, in which a pin 2 is rotatably mounted which atits outwardly and downwardly directed end carries a mouthpiece 3. Theouter end of the pin 2 carrying the mouthpiece 3 is bent in such amanner that the axis of the pin 2 intersects the axis of the mouthpiecein a point in the vicinity of the lower end of the mouthpiece intendedto be engaged with the surface of the workpiece. Through this mountingof the mouthpiece it becomes easier to engage the latter sealingly withthe workpiece than if the mouthpiece were rigidly mounted on the handle,and since the axis of the pin 2 will substantially extend through thearea of contact between the mouthpiece and the workpiece, a stableengagement of the mouthpiece with the workpiece is obtained. Thedescribed mounting of the mouthpiece could also be replaced by anotherform of articulated joint, which might comprise a universal joint, ifdesired.

The detailed construction of the mouth-piece is apparent from Figs. 2, 3and 4. As will be seen, the mouth piece consists of a metallic sleeve 4,at the front end of which an .elastic sleeve 5, e. g. of a plasticmaterial not subject to damage from electrolyte, is provided. Themetallic sleeve 4 is constructed with two co-axial passages, the innerone 6 of which is formed by a tube 7 extending through the metallicsleeve and serving at its outward and as a fitting for the connection ofaflexible tube 8. The outer passage 9 is formed by a bore in themetallic sleeve, in which there is mounted an inclined upwardly directedpipe for the connection .of a flexible tube. The passages 6 and 9 areopen at the bottom end of the metallic sleeve .4, below which a chamber11 is formed, which is surrounded by the elastic sleeve 5. 'In the mouthof the passage '9 there is provided a flange 12, which may be integralwith the tube 7, and is constructed with a plurality of inclined passageopenings 13. A flexible tube 14 is connected to the :pipe:8 anda'flexibletube 1510 the pipe 10. Both :of .these'flexible tubes extendlengthwise through the mouthpiece and are continued from the rear end ofthe latter by suitable lengths of flexible tube for connection toanapparatus for causing an electrolyte to flow through the flexible tube.15

and the mouthpiece 3 and back through the flexible tube 14.

A lever 16 is pivoted to the handle at '17 and has one end thereofextending upwards from the handle, while at its other end carrying aroll 18 serving as a squeezing member for squeezing the flexible tubes14 and 15. To

the -'arm of the lever 16 extending upwards from-the pivot 17 there isconnected a compressional spring 19. This compressional spring tends tokeepthe lever 16 in the position shown in the drawing, ,in which theroll 18 squeezes the flexible tubes 14 and and thereby prevents thecirculation of electrolyte through the latter. By means of a finger ofthe hand, in which the handle is held, the lever 16 can be moved to theposition shown in dotted lines, in which the roll 18 liberates theflexible tubes 14 and 15 so as to permit electrolyte to circulatethrough the latter.

In the handle there is also mounted a pair of contact springs 20, one ofwhich is provided with a nose 21'lying in the path of the lowerend ofthe lever 16, so that the "latter will strike the nose 21 and therebyclose the contacts .towards the end of its movement from the positionshown in full lines to the position shown in dotted lines.

The contact springs are interposed in a conductor 22 from one terminal'23 of a source-of electric current to the pin 2 and thereby to themouthpiece 3. 'To the other terminal 24v of the source 0f electriccurrent there is connected a conductor'ZS intended-for conthe handle 1and applies the mouthpiece 3 to the spot of the workpiece, whereit isdesired to perform an electrolytic polishing. The elastic sleeve 5 isfirmly engaged with the workpiece-and owing toits .elasticity iscapableof adjusting itselftothe shapethereof so that'it will be possible tortreat notonlyplane surfaces-but alsosu-rfaces having a certain amountof curvature in one or more directions. By means of a finger of thehand, in which the handle 1 is held, the lever 16 is moved from theposition shown in full lines to the position shown in dotted lines. Themore the lever approaches the last named position, the shorter will bethe arm on which the compressional spring 19 acts, and consequently onlya relatively small force will be needed for keeping the lever in theturned down position in which it is to remain as long as theelectrolytic polishing is being conducted. As soon as the squeezing ofthe flexible tubes 14 and 15 under the influence of the roll 18 ceases,electrolyte will commence to circulate from the flexible tube 15 throughthe mouthpiece 3 to the flexible tube 14. The electrolyte enters intothe mouthpiece through the pipe 10 and then flows through the outerpassage and the inclined passage openings 13 into the chamber 11 andfrom there back through the inner passage 6 to the flexible tube 14. Aswill be seen, the flow of electrolyte in the chamber 11 is directedinwardly from the circumference, while at the same time the passagethrough the inclined openings 6 '13 imparts a circular movement to theelectrolyte. 'It has been found that this type of flow will result in asuitable sweeping of the'whole of the area=surrounded by the elasticsleeve 5 so that a uniformpolishing is obtained over substantially thewholeof the area ofithe workpiece covered by the opening .of themouth-piece.

The electrolytic polishing can only be started from the moment when the'lever .16 closes the contacts 20, and is interrupted again assoonas-the lever ;16 is released, whereby the electric circuit is .firstinterrupted and the flexible tubes 14 and '15 are thereafter squeezed bymeans of the roll 18 so that also the liquid .circuitis interrupted,whereafter the mouthpiece can be lifted away from the surface of theworkpiece. It is to 'be observed that the contacts-20 are only intendedas.a safety switch, the control of the current being normally performedat a current supply equipment having a timing arrangement. If no suchcurrent supply equipment is available, or it is in special circumstancesinconvenient to use it, the control of the current may be performed 'bymeans of the contacts 20. It will be seen that the roll '18 in :theprocess of squeezing the flexible tubes 14 and .15 will sweep along thelatter in a direction away from the mouth-piece whereby the electrolyteis slightly sucked away fromthe mouthpiece and theztendency to drippingfrom the latter is consequently minimized. During .the return stroke ofthe lever 16, the arm on which the compressional spring 19 actsbecomesgradually longer, :while at the same time the arm, on which theresistance of .the flexible tubes against squeezing acts, becomesgradually shorter so thata very efi'icient squeezing .is obtained in thefinal position of this movement indicatedin full lines in the drawing.

:Figs. ,5 and 6 show an apparatus that maybe used to obtain thecirculation of electrolyte. The apparatus con sists of a case 26 inwhich two tanks 27 and 28 are mounted. The case is intended to be placed-.in either one of two different positions shown in :Figs. 5 and6:respectively, and is provided with two'handles 29 and 30, by means ofwhich the case can beplaced or carried in one and the other of these two'positionsirespectively.

Tubes 31 and32 are connected to the tanks '27 :and'28, of which tubesthe tormerextends from 'the bottom of the tank '27 whenthecase-is,inthe'positionillustrated in Fig. 5, while the tube '32 extends downinto the tank28 from the upper end thereof. The tubes 31 and 32 :areintended for the connection of :the flexible tubes '15 and 14respectively, and it will be seen that when electrolyticliquidispresent-in the tank 27, this-willbe capable, owing to thedifference of level betweenthe tanks 27 and 28, to flow through the tube31, the flexible tube '15, the mouthpiece 3, the flexible tube 14'an'dthetube '32 down into the tank '28. As long as the whole tubesystem is full of electrolyte, this flow-will be independent ofthelevelat which the handle with=the mouth piece is held relative to thecase. A tube 33 is also provided directly between the tanks 27 and 28,the said tube being connected in such a manner that in the position ofthe case shown in Fig. 5 there will be no flow of electrolytetherethrough. On the other hand, in the position of the case illustratedin Fig. 6, the tube 33 connects the bottom end of the tank 28 with thebottom end of the tank 27, and since in this position the tank 28 islocated at a higher level than the tank 27, the electrolyte will flowfrom the tank 28 to the tank 27 so that the system is thereafter readyfor being used again in the manner illustrated in Fig. 5.

Fig. 7 shows another example of an apparatus, by means of which the flowof electrolyte may be created. In this figure, 34 and 35 are two tanks,of which the tank 34 is sealingly closed, while the tank 35 is in opencommunication with the atmosphere through a tube 36. The tube 36 is solocated, and the maximum quantity of liquid in the tank 35 so selected,that the liquid cannot end. Moreover, the flexible tube 15 is connectedto the tank 35 and the flexible tube 14 to the tank 34.

The function of the apparatus illustrated in Fig. 7 is as follows:Before the apparatus is taken into use, a certain quantity of liquid ispresent in each of the tanks 34 and 35. If a pressure is now exerted onthe rubber ball 37, a pressure above that of the atmosphere is producedin the tank 34, and under the influence of this pressure electrolyte ispressed through the pipe 38 into the tank 35, which latter remains atatmospheric pressure because it is in open communication with theatmosphere through the tube 36. When releasing the rubber ball 37, thelatter will again expand to its normal shape and will therefore producea vacuum in the tank 34, because the valve 39 prevents a return flow ofelectrolyte from the tank 35 to the tank 34. The apparatus is now readyfor carrying out an electrolytic polishing. When the flexible tubes 15and 14 are opened by means of the lever 16 of the handle 1, electrolytewill flow from the tank 35 through the flexible tubes 15 and 14 and themouthpiece lying between the latter to the tank 34 under the influenceof the pressure difference between the tanks 34 and 35. If during theelectrolytic polishing the mouth piece happens to be lifted a littlefrom the surface of the work piece, no electrolyte will flow out,because the mouth piece is at a vacuum.

We claim:

1. An apparatus for electrolytically polishing limited surface portionsof a metallic workpiece, comprising a handle, a mouthpiece mounted onsaid handle, said mouthpiece having an open end to be applied to theworkpiece and being constructed with two co-axial passages opening at asmall distance behind said open end, a source of electrolyte, conduitmeans including flexible conduit portions connecting said two passagesindividually with said source of liquid electrolyte, means forcirculating electrolyte from said source to the outer one of said twopassages and back through the inner one of said two passages to saidsource, manually operated means mounted on said handlefor selectivelypermitting and cutting olf said circulation of electrolyte, and anelectric circuit for creating a potential difference between theelectrolyte and the workpiece.

2. An apparatus as in claim 1, in which said mouthpiece is mounted on apin mounted in said handle for rotation about an inclined axisintersecting the axis of said mouthpiece in a point substantially in theplane of the open end thereof.

3. An apparatus as in claim 1, in which said conduit means compriseflexible liquid conduits extending from said mouthpiece through saidhandle, and said manually operated means comprise means for squeezingsaid tubes in a direction away from said mouthpiece to cut off the flowof electrolyte.

4. An apparatus as in claim 3, in which said manually operated meanscomprises a lever pivotally mounted in said handle and having one endthereof projecting externally of said handle to form an operatingmember, and a roller mounted at the other end of said lever forcontacting said flexible conduits to squeeze the same.

5. An apparatus as in claim 4 including a spring biasing said levertowards the position at which said conduits are closed, the pivotalmovement of said lever toward non-squeezing position decreasing theelfective moment arm of the spring with respect thereto.

6. An apparatus as in claim 1 including guiding means provided in theouter one of said two co-axial passages for imparting circular movementabout the axis of the mouthpiece to the liquid electrolyte emerging fromthe annular opening of said outer passage.

7. An apparatus as in claim 1, in which the wall of the part of saidmouthpiece extending beyond the mouths of said co-axial passages isformed of an elastic material.

8. An apparatus as in claim 1, in which said electric circuit includes aswitch mounted on said handle, which switch is closed by said manuallyoperated means towards the end of its movement to permit flow ofelectrolyte.

9. An apparatus as in claim 1, in which said source of electrolytecomprises two tanks, one of which is closed from the atmosphere andincludes a manually operable resiliently compressible compartment, whilethe other tank is in open communication with the atmosphere, a conduitconnection between the two tanks, said connection comprising a valvewhich permits a flow of liquid only in the direction from the closedtowards the open tank, said conduit means connecting the outer one ofsaid two co-axial passages with said open tank and connecting the innerone of said two co-axial passages with said closed tank.

References Cited in the file of this patent UNITED STATES PATENTS2,080,234 Schlotter May 11, 1937 2,698,832 Swanson Jan. 4, 1955 FOREIGNPATENTS 672,698 Germany Mar. 8, 1939 921,192 France Jan. 10, 1947 26,504Great Britain Nov. 18, 1912.

1. AN APPARATUS FOR ELECTROLYTICALLY POLISHING LIMITED SURFACE PORTIONOF A METALLIC WORKPIECE, COMPRISING A HANDLE, A MOUTHPIECE MOUNTED ONSAID HANDLE, SAID MOUNTHPIECE HAVING AN OPEN END TO BE APPLIED TO THEWORKPIECE AND BEING CONSTRUCTED WITH TWO CO-AXIAL PASSAGES OPENING AT ASMALL DISTANCE BEHIND SAID OPEN END, A SOURCE OF ELECTROLYTE, CONDUITMEANS INCLUDING FLEXIBLE CONDUIT PORTION CONNECTING SAID TWO PASSAGESINDIVIDUALLY WITH SAID SOURCE OF LIQUID ELECTRLYTE, MEANS FORCIRCULATING ELECTROLYTE FROM SAID SOURCE TO THE OUTER ONE OF SAID TWOPASSAGES AND BACK THROUGH THE INNER ONE OF SAID TWO PASSAGES TO SAIDSOURCE, MANUALLY OPERATED MEANS MOUNTED ON SAID HANDLE FOR SELECTIVELYPERMITTING AND